(1) Field of the Invention
The present invention relates to a method and apparatus for the separation of materials having different densities in a mixture of the materials to allow for use or disposal of the different materials. In particular, the present invention relates to a method and apparatus for separating sand, which is used for bedding animals, such as cows, from manure in a sand and manure mixture to allow for easy disposal of the manure and reuse of the sand. The present invention also relates to a method and apparatus for use in the mining industry to separate materials having different densities.
The use of sand as a bedding for animals such as cows has become increasingly more widespread. It has been found that the use of sand as a bedding material for cows has several advantages over the traditionally used chopped straw, sawdust or wood shavings. Some of the benefits are improved udder health, increased cow comfort, cleaner cows, improved traction and lower cost. One drawback to the use of sand is the significant handling and storage problems associated with the resulting manure and sand mixture. The sand in the mixture obstructs the pumps normally used to irrigate the manure suspension onto the surrounding ground surface. Further, when the mixture is filled into pits, the sand eventually settles out of the mixture and fills the pit thus, requiring another pit or excavation of the pit. Either method of disposal is costly which can negate the benefits associated with the use of sand. To allow for easy disposal or storage of the mixture, the manure and sand must be separated. In the past, there was no quick and inexpensive way of separating the manure from the sand.
(2) Description of the Related Art
The related art has shown an assortment of liquid and solid separation systems common to waste water treatment operations as well as the dairy, mining and petroleum refining industries. The publication "Handling and Storage Systems For Sand-Laden Dairy Manure From Free Stall Barns", The Proceedings of the Third International Dairy Housing Conference, Dairy Systems for the 21st Century, 1994 ed. Ray Bucklin, American Society of Agricultural Engineers by some of the inventors describes the current methods of handling sand-laden dairy manure and of separating sand from sand-laden dairy manure. The paper also describes the characteristics of a settled sand profile and provides suggestions for long term handling and storage of sand-laden dairy manure. In addition, the publication, "Analysis of a Batch Aerated Grit Chamber Used to Separate Bedding Sand From Dairy Manure" 1995 ASAE Annual International Meeting Paper No. 95-4705 by the inventors describes several liquid, solid separation techniques and their effectiveness in separating sand from manure in a sand and manure mixture.
Some separation systems such as screening and dissolved air floatation are ineffective for use in separating manure and sand. Screening is ineffective due to the similarities in the particle size distributions of bedding sand and manure. Dissolved air floatation is ineffective because the minute bubbles are unable to float the large, coarse manure particles to the top of the tank for removal. Some other separation systems such as sedimentation and the hydrocyclone are more effective but have disadvantages. Sedimentation is an effective sand separation technique. However, the sand and manure settle out as layers with the manure on top of the sand. The layer of manure on the sand makes removal of the sand difficult without also removing the manure. In addition, dilution ratios in excess of 1:1 (mass parts of water to mass parts of sand laden manure) are required to separate a significant amount of sand from the manure. The separation does not increase for dilution rates greater than 3:1. Hydrocyclones have the potential to be effective sand separators. However, to be effective, the solid feed concentration must remain constant which is difficult to achieve with the manure and sand mixture.
Applications of aeration such as the Pachuca tank and continuous flow aerated grit chambers might also be used to separate sand from manure. However, the prior art does not disclose any such applications using these methods for the stated materials. Pachuca tanks are circular vessels with conical bottoms. Air is introduced at the apex of the conical bottom. The purpose of the conical bottom is to redirect settled solids into the upward flowing fluid so that they may be resuspended. However, because the manure and the sand co-exist in coagulated clumps of a large size, the effectiveness of this technique is reduced. Continuous flow aerated grit chambers consist of either a circular or rectangular concrete tank with air diffusers positioned above the bottom of the tank. The chamber operates as follows: i) influent waste water containing water, organic matter and grit enters the tank; ii) the energy inputted to the water by a continuous air flow creates hydraulic movement of the water; iii) grit settles out while organic material is kept in suspension and carried out of the tank; iv) the accumulated grit is then removed immediately from the tank; and v) effluent containing water and suspended organic matter flows out of the tank. The nature of the energy adsorption into the fluid is crucial to effective grit removal.
The related patent art has also shown various methods and apparatus for separating different materials having different sizes or weights using air and water to provide agitation to separate the materials. Illustrative are U.S. Pat. Nos. 2,933,187 to Old et al; U.S. Pat. No. 4,324,652 to Hack and U.S. Pat. No. 4,851,036 to Anthes et al.
Old et al describes an apparatus used for the floatation separation of particles, specifically concrete. The apparatus consists of a tank having an inclined bottom along which is mounted a combination agitator and conveyor. Water and air are introduced vertically into the deep end of the tank and the feeding of the material to be separated is downward into the tank opposite the air and water. In the separation process, the lightweight material floats and is discharged over the wall of the tank at the deep end. The heavier particles are moved along the tank upwardly toward the remote end where it is discharged. A removable, vertically oriented screen extends across the tank, intermediate the ends of the tank and prevents the lightweight material from moving with the heavy material toward the shallow end of the tank.
Hack describes a method and apparatus for scrubbing crude oil (bitumen) from tar-sands. The apparatus includes a pair of counter-rotating screw conveyors which tumble the tar-sand so as to rub the grains together and scrub the oil from the sand particles while at the same time moving the progressively cleaner sand toward the discharge end. An air-aspirating venturi underneath the sand lying in the bottom of the cell allows for simultaneously flushing and aerating the sand being tumbled to push the oil particles through the sand and carrying them to the surface.
Anthes et al describes a process and apparatus for separating relatively floatable particulate material from a mixture also having relatively non-floatable, particulate material. The apparatus includes a column with at least one baffle to promote turbulence within the column. Air is introduced into the column below the point of introduction of the mixture to be separated. Water is also added to the column. The rates of introduction of the mixture, air and water and the number and configuration of the baffles must be such as to create a substantial amount of turbulence in the column to keep the relatively floatable particulate matter at the upper portion of the column.
Also of interest is U.S. Pat. No. 4,617,113 to Christophersen et al which shows a floatation separating system. Only of minimal interest are U.S. Pat. Nos. 2,168,942 to McClave; U.S. Pat. No. 4,297,208 to Christian and U.S. Pat. No. 5,368,731 to Pesotini.
There remains a need for an apparatus which easily and quickly separates the materials having different densities in a mixture of the materials to allow for use or disposal of the different materials.